The novel benzamide derivative YM 43611 is a selective dopamine D3/D4 receptor antagonist with an in vitro profile of effects suggestive of atypical antipsychotic activity. In this study the effects of YM 43611 were compared with those of the conventional antipsychotic haloperidol and the atypical antipsychotic clozapine in behavioral studies with squirrel monkeys. Like haloperidol and clozapine, YM 43611 induced dose-related decreases in response rate under a fixed-interval schedule of stimulus-shock termination. Like halopeidol, but unlike clozapine, YM 43611 also antagonized the behavioral effects of (+)amphetamine in a surmountable manner and induced dose-related increases in static and unusual postures indicative of catalepsy. Both YM 43611 and haloperidol failed to substitute for clozapine in monkeys trained to discriminate clozapine from vehicle. Although YM 43611 appears to have in vitro effects predictive of atypical antipsychotic activity, its in vivo effects in primates were qualitatively similar to those of the conventional antipsychotic haloperidol.